1. Technical Field
The present invention relates to a communication device for receiving a signal through a propagation channel and, in particular, to a communication device for compensating distortion in a propagation channel by a simple construction or a simple processing.
In addition, the present invention relates to an effective technology for identifying a received signal of each of plural other communication devices when receiving signals from the plural other communication devices.
2. Background Art
For example, it has been well known that when the wireless transfer function of expressing distortion in a wireless propagation channel can be extracted, the function of its inverse characteristics can be produced to be able to cancel characteristic degradation in the wireless propagation channel with large effect. However, a processing capacity required to find the wireless transfer function is high, so that it is difficult to realize the wireless transfer function in an actually operated wireless system. Hence, there are few examples of bringing the wireless transfer function into practical use.
In FIG. 7, a construction example of a receiver is shown as one construction example in which propagation channel distortion compensation is applied to a base station device (W-CDMA base station device) employing a W-CDMA (Wideband-Code Division Multiple Access) system of a 3GPP wireless system of a global standard.
The W-CDMA base station device of this example includes: a received data storage memory 21; a subtractor 22; a channel synchronization control section 23; a pilot channel inverse diffusion function section 24; a phase control section 25; a data inverse diffusion function section 26; a multiplier 27; a RAKE synthesis section 28; a demodulation section 29; a replica control section 30; a data hard-determination section 31; a path multiplication section 32; a multiplier 33; a diffusion function section 34; a replica storage-memory 35; a propagation channel distortion storage memory 36: and a subtractor 37.
Here, the function sections added so as to compensate distortion in the propagation channel are, for example, the received data storage memory 21, the replica control section 30, the data hard-determination section 31, the path multiplication section 32, the multiplier 33, the diffusion function section 34, the replica storage memory 35, the propagation channel distortion storage memory 36, and the subtractor 37.
One example of the operation performed by the W-CDMA base station device of this example will be described.
Received signals (received data) from a certain terminal device (for example, terminal device 1) are inverse diffused by the data inverse diffusion function section 26, and a pilot channel is inverse diffused by the pilot channel inverse diffusion function section 24, and phase compensation (complex multiplication, in this example) is performed to the result of the inverse diffusion performed by the data inverse-diffusion function section 26 by the phase control section 25 and the multiplier 27 on the basis of a phase rotation amount computed from the pilot channel, and the synthesis of multiple paths is performed to the result of the phase compensation (RAKE synthesis) by the RAKE synthesis section 28. In this case, the synchronization of the received signals is achieved by the channel synchronization control section 23, whereby the synchronous timing of the pilot channel inverse diffusion function section 24 and the data inverse diffusion function section 26 is controlled.
Here, when the synthesis result obtained by the RAKE synthesis section 28 is inputted to the demodulation section 29 as it is, there is provided a usual signal processing to which propagation channel distortion compensation is not performed.
On the other hand, when the propagation channel distortion compensation is performed, the value (0, 1) of the data is determined by the data hard determination section 31 (data hard determination) on the basis of the synthesis result obtained by the RAKE synthesis section 28 and the determination result is copied for each of multiple paths. The multiple paths produced by the copying are multiplied (complex multiplied in this example) by the phase rotation amount found by the phase control section 25 and the multiplication results are again diffused by the diffusion function section 34.
With this, an ideal signal (replica) estimated to be transmitted from the concerned terminal device (terminal device 1, in this example) can be produced and the replica is stored in the replica storage memory 35.
This replica is subtracted from the entire received signals (entire received data) by the subtractor 22, and then on the basis of the subtraction result, in the same way as described above, the inverse diffusion, the phase compensation, and the RAKE synthesis are performed to a received signal from the other terminal device (for example, terminal device 2) and further the hard determination, the path multiplication, the phase rotation, and diffusion are performed to the data to thereby produce a replica. Then, in the same way as described above, the replica of the terminal device 1 is further subtracted from the entire received signals from which the replica of the terminal device 1 is subtracted.
Thereafter, in the same way, the replica of the terminal device 3 is subtracted from the entire received signals . . . , then, the replica of the terminal device 4 is subtracted from the entire received signals . . . and so on . . . , in other words, the replicas of all terminal devices from which data is to be received are subtracted from the entire received signals. As the result, the wireless transfer function of expressing distortion in the propagation channel can be found.
In this regard, the number of productions of the replica is controlled by the replica control section 30, whereby the input to the subtractor 22 is set on or off and the destination of output from the RAKE synthesis section 28 is switched and controlled.
The results obtained by subtracting the replicas of all terminal devices, from which data is to be received, from the entire received signals are stored as the results of found distortion in the propagation channel in the propagation channel distortion storage memory 36. These results are subtracted from the entire received signals by the subtractor 37 to thereby cancel (compensate) the propagation channel distortion of the entire received signals.
Then, for example, when the data of the terminal device 1 is acquired, all replicas of the terminal devices 2 and subsequent terminal devices (in other words, replicas of all terminal devices except for the terminal device 1) and the propagation channel distortion are subtracted from the entire received signals, and then the inverse diffusion, the phase compensation, the RAKR synthesis, and the demodulation processing are performed to the results, whereby an optimal solution can be obtained.
Further, in the above-mentioned processing, the produced replicas can contain errors caused by the distortion and hence cannot be perfect. Still further, the propagation channel distortion found by the use of the replicas cannot be also perfect. For this reason, the procedure of producing a replica again on the basis of the received signal obtained by subtracting the propagation channel distortion that has been once found is repeatedly performed. With this, the propagation channel distortion and replica that contain fewer errors can be produced and hence the received data that contain fewer errors can be found. When this procedure is repeatedly performed to make errors converge, ideal characteristics can be obtained.
Patent document 1: JP-A 2003-115786
Patent document 2: JP-A 2003-519962
Patent document 3: JP-A 2005-516442